The invention relates to a reactor for catalytic reformation of hydrocarbons with steam under elevated pressure to produce synthesis gas. Synthesis gas of this kind, for example, serves to produce ammonia, hydrogen, and methanol.
Reactors for catalytic reformation of hydrocarbons with steam have been known for a long time and are known in a multitude of layouts. For large-capacity plants, a design has paved its way in which a top-fired box-type furnace with upright standing reaction tubes and/or split tubes is implemented. The split tubes are arranged in series. The tubes are passed through from top to bottom by process gas which forms the input gas. The input gas is subjected to a so-called splitting process.
The gas outlet temperatures usually range at 850° C. and beyond. In the lower area—inside or outside the furnace—the process gas is collected in so-called outlet collectors. Burners firing vertically downwards are arranged in the “lanes” lying between the tube rows. This area is designated as furnace box. Generated flue gas streams from top to bottom through the furnace and is discharged through so-called flue gas tunnels lying at the bottom. On average, the temperatures in the furnace box range between 1000 and 1250° C. For thermal insulation and for protection from high temperatures prevailing due to heating, the furnace walls are lined with a protective refractory lining.
The reaction space heated by the furnace usually comprises a multitude of gas-proof sealed vertical tubes arranged in rows and being suitable for being filled with a catalyst. These serve for process management and they are equipped with facilities for supplying hydrocarbons to be reformed and steam heated-up to 650° C. to the reaction space as well as facilities for discharging the reformed synthesis gas from the reaction space.
In its lower area, the furnace space in which the firing devices are arranged has a chamber for collection of flue gases as well as a multitude of mainly horizontally arranged bricked tunnels extending in parallel to each other and perpendicular to the vertical tubes for discharge of flue gases. At their sides, these bricked tunnels have apertures to allow a discharge of flue gases from the furnace space. The tunnels are usually bricked-up of masonry materials.
WO2005/018793 A1 describes a typical furnace system and a method for catalytic reformation of hydrocarbons with steam at elevated pressure to obtain synthesis gas. A special configuration of the external walls of the tunnels is applied in order to achieve a better homogenization of the flue gas flow and to obtain a more uniform temperature distribution of the furnace firing. WO2005/018793 A1 describes a typical furnace system and a method for catalytic reformation of hydrocarbons with steam to obtain synthesis gas by supplying oxygen to adapt the stoichiometry and with a special pore burner installed further downstream to avoid formation of soot.
All the reforming systems described hereinabove have in common that a firing device comprised of a multitude of burners arranged between process managing reaction tubes heats the oven space with the reforming tubes leading through the furnace space. Burners serving for firing the oven space are usually supplied with fuel gas and air through separate channels. The supply of fuel gas into the burner space is accomplished separately from the supply of air. The penetration of gas feeders into the burner space is accomplished through the refractory furnace lining or immediately in front of it. With hitherto applied designs, the ratio between fuel gas and air for the burners is controlled by a butterfly flap or a similarly designed facility for the adjustment of the gas flow of the air supply. The burner firing and thus the furnace temperature can be controlled via this facility. Though this design is efficient, it bears a disadvantage in that the local air supply at the burners can be poorly controlled and leads to unfavorable ratios between fuel gas and air in some isolated cases.
The ratio between oxygen and fuel gas can technically be described by the so-called Lambda (λ) value. On applying a stoichiometrical mol ratio of oxygen versus fuel gas, one obtains a Lambda value of 1.0. On using an oxygen portion which is lower in the stoichiometrical combustion ratio, one obtains a Lambda value which is lower than 1.0. Applying an oxygen portion which is higher in the stoichiometrical combustion ratio, one obtains a Lambda value which is higher than 1.0. Therefore, combustion is optimal if the Lambda value amounts to 1.0. With conventional designs, one obtains Lambda values at the individual burners which fluctuate due to operation and which may have temporarily higher values.
This takes an adverse effect on the combustion process. Its consequence may be a higher total consumption of fuel gas relative to the turnover of the reforming process. With a change of the fuel material, the supply of air can hardly be adjusted to the modified stoichiometry. Consequently, it may temporarily entail an unintentional increase in the flame temperature and, as a result of an increased inflow of air, it may involve an intensified formation of nitric oxides of the NOx type. As pollutants in the atmosphere, nitric oxides contribute to acid rain.